Forget the small screen and the big screen. The hottest new thing in television is the “second screen” — the one on the tablet computer or cell phone that an increasing number of viewers keep an eye on while they’re watching TV. And figuring out how to corral all those second-screeners and make money off them was the hottest topic as a convention of 5,000 television executives in Miami Beach on Tuesday.

“This is really the hottest thing in television now,” said Trevor Doerksen, founder of the Canadian on-line marketing company Mobovivo. “Everybody — advertisers, producers, TV networks — everybody wants to grab those second-screeners.”

Doerksen spoke at one of several panel discussions of the second-screen phenomenon at the convention of National Association of Television Program Executives, which ends its three-day run at the Fontainebleau Hotel on Wednesday. The convention has traditionally been a swarming marketplace for the sale of syndicated TV programming, but this year much more of the buzz has been about how viewers watch television rather than what they see.

Nowhere is television’s simultaneous convergence and competition with the Internet more obvious than it is in second-screen. By some industry counts, as much as 30 percent of web-surfing is done while watching TV. If those viewers are drifting away to check their email or gaze idly at breaking news sites, that’s a threat to the TV industry. But if they’re using their computer to enhance their TV viewing — by learning more about the show or chatting it up with friends — it’s an opportunity.

Much of the talk at the NATPE convention was about how to direct viewers to second screens using new computer applications, a process the industry calls “social television.”

“If you’re a network or a producer, you want to keep those second-screeners watching your show rather than going off in some other direction,” said Doerksen. His app Previiw — which will launch on networks in the United States and Canada later this year, he says — pulls together material from various websites as well as Facebook and Twitter so a user can quickly look up the history of any character appearing on-screen at a given moment as well as biographical details of the actor playing him and any recent tweets or other Internet postings he’s made.

Like other television apps, Previiw is “audio-synched” — that is, it listens to your television through the microphone in your computer, uses audio fingerprints to figure out what show you’re watching, and then synchronizes itself to the exact point in the episode that’s on your TV screen. The audio-synch function makes Previiw work even with shows recorded on a DVR or watched on a DVD.

Another new app, Get*This, tells viewers how to buy stuff they see during TV shows. “It’s all about Rachel’s blue sweater from Friends that everybody wants,” said Lisa Farris, the company’s founder. A viewer watching American Idol who’s smitten with a young performer’s guitar could use her app to discover, ‘Oh, it’s a $2,000 guitar. But, oh, there’s a $400 version.’”

Shawn Cunningham’s YapTV.com allows users to see what’s being said on Twitter or Facebook about whatever shows are on TV at the moment — all of them. And it compiles data from its users’ clicks to constantly post lists of what’s hot or what not. “On the last seven episodes of American Idol last season, we successfully predicted who was going to get kicked off,” he said.